Isometric imaging system

ABSTRACT

An isometric imaging system for effecting the projection of a three-dimensional coordinate system onto the horizontal and vertical plane of a conventional display scope is provided. The system provides for displaying both spatial and depth information by the novel transformation of the time coordinates of the scanned field, which contains the object, to the horizontal and vertical coordinates of the display scope. In one embodiment a novel sample and hold circuit is provided for processing data on tapes at playback factors greater than 10.

United States Patent Becker et al.

[ Feb. 12, 1974 ISOMETRIC IMAGING SYSTEM Inventors: Frederick L. Becker;Richard L.

Trantow, both of Richland, Wash.

Assignee: The United States of America as represented by the U.S. AtomicEnergy Commission, Washington, D.C.

Filed: May 24, 1972 App]. No.: 256,300

U.S. Cl 340/5 MP, 73/67.7, 343/79 Int. Cl... G0ls 9/66 Field ofSearch... 340/3 C, 3 R, 5 MP; 343/79;

References Cited UNITED STATES PATENTS 3,044,058 I 7/l962 Harris 343 79TRANSLATION STAGE INDEXING CIRCUITRY TRANSLATION STAGE POSITION SENSORSy W X ULTRASONIC TRANSMITTER RECEIVER CLOCK Primary ExaminerRichard A.Farley Attorney, Agent, or Firm.lohn A. l-loran 3 Claims, 3 DrawingFigures ISOMETRIC DISPLAY GENERATOR Z AXlS (a WDEO g TRIGGERABLE PULSE 1DETECTOR GENERATOR i PATENTEU FEB 1 21974 SHEET 3 0F 3 wil 82 9+ 3. E mow l 2+ 9 .H A H A N O V ISOMETRIC IMAGING SYSTEM BACKGROUND OF THEINVENTION The invention described herein was made in the course of, orunder, a contract with the U. S. Atomic Energy Commission. It relatesgenerally to imaging systems and more specifically to an isometricimaging system.

Heretofore various techniques have been devised in the electronicart forimaging viewed objects. These have included, for example, bothtwo-dimensional and true three-dimensional display systems. Wherethreedimensional imaging systems have been devised, dual cathode raytube (CRT) displays have been generally utilized. Such is the case insonar display systems. In the area of detecting and mapping objects inopaque liquids, as well as non-destructive testing of solids forinternal flaws, ultrasonic imaging, which typically utilizes Thisdetected signal is finally recorded as a single point on a recordingdevice which is scanned in synchronization with the transducer. TheB-scan technique is similar except that time or depth information from asingle cross section is displayed on the face of a cathode ray tube(CRT). In the case of both the B and C- scan techniques, the resultingimage is a flat pattern of the viewed object. Hence, both of theseexcellent analytical tools suffer a basic shortcoming in the fact thatboth spatial and depth information cannot be displayed on a singlerecord. Accordingly, in the specialized area, for example, of evaluatingthe true nature of an unknown object or flaw these techniques leave muchto be desired.

The discovery of holography, both optical and ultrasonic, for imagingviewed objects has afforded basic improvements over the earlierdeveloped ultrasonic B- and C- scan techniques. With ultrasonicholography both spatial and depth information are recordedsimultaneously but it does not, however, produce a threedimensionalimage as is in fact produced in optical holography due to the differencein wave length between the ultrasound and the laser light used in thereconstruction of the hologram. The inability to focus thereconstructing lense at only one particular depth while all other depthsremain out of focus presents limitations to ultrasonic holography as ananalytical tool, as well as the considerable cost associated with such atechnique.

It may thus be seen that while many excellent imaging systems have beendevised it is desirable to have an inexpensive imaging system whichaffords the displaying of both spatial and depth information about aviewed object.

SUMMARY OF THE INVENTION wherein spatial and depth information of aviewed object are recorded simultaneously as an isometric projection ona display.

Still another object is to provide an ultrasonic imaging system forviewing objects in opaque liquids, such as liquid sodium.

A further object of this invention is to provide an imaging systemwherein the image of the viewed object may be rotated and/or tilted toobtain optimum perspective.

Still a further object is to provide an economical, easy to operateimaging system which utilizes an isometric projection of a viewed objecton a twodimensional display device, generally a cathode ray tube.

Another object is to provide an ultrasonic isometric imaging systemuseful in detecting flaws in solids.

A feature of the present invention is a novel isometric display circuit.

Other objects of the present invention will become apparent to thoseskilled in the art as the description proceeds.

The present invention generally comprises an isometric scanning systemas hereinafter described by reference to several drawings depicting theseparate features and/or combination of the separate features for theoverall system.

BRIEF DESCRIPTION OF THE DRAWINGS To facilitate an understanding of theinvention, reference is made to the several drawings of which:

FIG. 1 is a block diagram of the present isometric imaging system usingultrasonic signals and in particular depicts an isometric projection ona display scope of stacked discs as the viewed object wherein thespatial and depth information thereof is readily apparent.

FIG. 2 is a schematic diagram of a circuit which transforms the X and Yposition voltages of the viewed object along with the Z axis rampvoltage to the X, Y time coordinates of a display scope.

FIG. 3 is a schematic diagram of a sample and hold circuit, whichsamples the Z axis signal and holds it at the amplitude whichcorresponds to the arrival of an incoming echo signal.

DESCRIPTION OF THE PREFERRED EMBODIMENT The block diagram given in FIG.1 depicts the present invention in a general fashion. While it is to beunderstood that the isometric imaging system may be utilized to depict avariety of signals, the invention will be described hereinafter withparticular regard to an isometric imaging system for depicting signalsgenerated by ultrasonic means such as would be useful in LMFBRapplications (i.e., under sodium viewing). For this any of the wellknown ultrasonic systems for viewing objects in opaque fluids may beused to generate to detect a given signal. One such embodiment maycomprise an ultrasonic transmitter-receiver 1, a transducer 2, and anX-Y scanner 3. An object 4 is positioned such that short ultrasonicpulses from transmitter-receiver 1 are reflected off the surface of theobject 4 and detected by transducer 2, the position of which iscontrolled by translation stage indexing system 5. The detected signalsare then amplified in the receiver section of 1 and time gated toinclude only those areas of the object to be imaged. A clock 6 which isa pulse generator controls the repetition rate of thetransmitter-receiver 1 and is the time reference from which all time ordepth information is measured. A delay generator 7 is adjusted for adelay equivalent to the transit time (down and back) of the highestelevation to be viewed and a pulse width equivalent to the depth offield of the desired image. Gate 8 then accepts echo signals 9 from thedesired depth ranges. The leading edge of this pulse is also used totrigger ramp generator 10. It should be seen that the height of the rampvoltage 11 at any point in time represents a particular depth of Z axiscoordinate.

The isometric projection 12 of the viewed object 4 is achieved on thedisplay scope 13 in accordance with the present invention, by feeding a(Z axis) ramp voltage 11, along with the X and Y position voltages 14,15 respectively, into the isometric display generator 16. The Xhorizontal signal 17 and the Y vertical signal 18 are connected to the Xand Y inputs of the display scope 13. The received ultrasonic echosignal 9 is time gated 8 and video detected 19. The video signal 20 isthen fed to a pulse generator 21 which modulates the display scope 13 torecord a dot at the X, Y coordinates which correspond to the X, Y, and Zcoordinates of the object 4 from which the echo signal 9 was reflected.

As may be seen from FIG. 1 the isometric projection 12 of the viewedobject 4 affords a clear and distinct advantage over the conventionallytransmitted C-scan which is characteristically quite flat, providing noperspective of the viewed object 4. Thus the serious drawback to C-scanor B-scan imaging that is the fact that both spatial and depthinformation cannot be displayed on a single record is obviated by thepresent invention. It will also be noted that the isometric projection12 of the entire object 4 is in focus with a highly accurate depthresolution. Accordingly, all of the advantages of a truethree-dimensional imaging system are obtained with the present isometricimaging system.

Referring to FIG. 2 there is shown a circuit for the isometric displaygenerator 16 which converts the X and Y position voltages 14 and 15 andZ axis ramp voltage 11 (i.e., time coordinates of the scanned field) tothe X horizontal signal 17 and the Y vertical signal 18 of the displayscope 13. This transformation is in accordance with the followingformulas:

Where is the rotation of the X, -Y axis and d) is the tilt of the Zaxis. Equation (1 and the terms inside the parentheses of Equation (2)correspond to a rotation of the object 4 while the cos (b and Z sin (1;terms appropriately modify the vertical perspective to correspond totilting of the object 4.

Referring to the circuit shown in FIG. 2 the X input voltage 14 whichrepresents the X coordinate of the transducer 2, is first multiplied bythe negative D.C. quadrature voltage of sin-cosine potentiometer 22 bymultiplier 23. The Y input voltage 15 which represents the Y coordinateis similarly multiplied by the negative D. C. quadrature voltage ofsin-cosine potentiometer 22 by multiplier 24. The outputs frommultiplier 23 and multiplier 24 are then summed by operational amplifier25 to provide the X output voltage 17. Operational amplifier 25 which isutilized in the unity gain inverting configuration is comprised of loadresistors 26, 27,

feedback resistor 28, capacitor 29 and balancing resistor 30.

The negative sin D. C. quadrature voltage of sincosine potentiometer 22is inverted by operational amplifier 31 and the resulting value ismultiplied by the X input voltage 14 using multiplier 32. Operationalamplifier 31 which is also utilized in the unity gain invertingconfiguration comprises load resistor 33, feedback resistor 34,capacitor 35, and balancing resistor 36.

The negative cosine D. C. quadrature voltage of sincosine potentiometer22 is multiplied'by the Y input 5 voltage by multiplier 37. The productis then summed with the product of multiplier 32 and the sum invertedusing operational amplifier 38 which is utilized in the unity gaininverting configuration and is comprised of load resistors 39 and 40,feedback resistor 41, capacitor 42 and balancing resistor 43. Theresulting sum is next multiplied by the negative quadrature voltage ofsin-cosine potentiometer 44 using multiplier 45.

The Z input 11 (value negative to provide an increasing time, i.e., morepositive ramp signal, equivalent to a negative going Z axis coordinate)is first multiplied by the positive cosine output of sin-cosinepotentiometer 44 using multiplier 46. The output of multiplier 45 isthen summed with the output of multiplier 46 and the sum inverted byoperational amplifier 47 which is comprised of load resistors 48 and 49,feedback resistor 50, capacitor 51 and balancing resistor 52, yielding Youtput 18. Equations 1 and 2 which represent the transformation depictedin the circuit shown in FIG. 2 may thus be seen to represent theprojection of a threedimensional coordinate system onto the X, Y planeof the display scope 13.

It will be appreciated by those skilled in the art that selection of thevarious components of the circuit employed to carry out the noveltransformation herein before described may 'vary over a wide range,depending generally on the frequency requirements of the X, Y inputposition voltages and Z axis ramp voltage. The circuit as shown in FIG.2, for example, will process X and Y position voltages up to 100 KHZ andZ axis ramp voltages up to 1 MHz with the following component selection:Operational amplifiers 25, 38 and 47 comprising an LM 201 which iscommercially available from National Semiconductor Corp; operationalamplifier 31 is a 334l which is commercially available from Burr BrownResearch Corp; multipliers 23, 24, 32, 37 and 45 comprising a mediumfrequency response device 432 J which is commercially available fromAnalog Devices Inc; multiplier 46 comprising a high frequency responsedevice 422 A which is commercially available also from Analog DevicesInc.

Advantageously this large bandpass is achieved by utilizing highfrequency operational amplifiers, multipliers and by multiplying thesignal by a DC quadrature voltage rather than passing the signal throughthe sincosine potentiometers. All of the multipliers are solid statedevices having outputs equal to the product of the two inputs divided by10. The divisor is used to limit the magnitude of the product.Operational amplifier 31 requires a load resistor 33 having a value atleast l0 times the input resistance of sincosine potentiometer 22.

Where such a high frequency capability is not required, componentselection is less stringent and may beneficially afford better highfrequency noise rejection.

In evaluating an image of an unknown object or flaw, it is highlydesirable to view the image from several perspectives withoutre-scanning the aperture. This can readily be accomplished, for example,by recording the X, Y, and Z information on an endless magnetic tapeloop and then playing it back at high speeds into the isometric displaygenerator 16. In this manner the rotation and tilt of the image may beviewed by adjustment of the controls of the isometric display generatoras the image is continuously regenerated. This feature of the presentinvention affords, advantageously, the selection of the optimumperspectives for evaluating the flaw or object in a relatively shortperiod of time without requiring re-scanning of the object. Moreover,ease of operation is assured in that the present system allows rotationof the imageas a function of only two angular parameters (6 and 4)) witha fixed relationship between the X and Y axis, as opposed to heretoforethree angular parameters.

Image regeneration times on rapid playback of re corded data depends ontwo factors, the original scanning time and the playback speed. When thetest or playback speed is increased, the signals are on the displayscope13 for a correspondingly shorter time. At normal speeds a pulse ofapproximately 2 p. seconds in duration from pulse generator 2l'isrequired to modulate the display scope 13; this is the lower limit of,for example, Textronics 61] display scope, commercially available fromTextronics Inc. For a scan time of two minutes and a tape speed increaseof 60, an image could, for example, be regenerated every 2 seconds. Ifthe repetition rate of clock 6 is lKHz and the playback speed isincreased by a factor of 60, the period of the ramp signal voltage 11would be less than 16 p, seconds, depending upon the delay time ofdelaygenerator 7. A 2 p. second modulation pulse from pulse generator 21would therefore considerably degrade the vertical resolution for thissituation in that the smallest resolvable element would be one-eighth ofthe total depth. A novel sample and hold circuit shown in FIG. 3 hasbeen devised for processing data at tape playback factors greater than10.

Referring to FIG. 3, the circuit consists, broadly, of three majorparts: A-discriminating pulse shaper detector, an integral circuitmonostable multivibrator and a solid state sample and hold module. Theinput to this circuit may be either the detected video signal or thegated echo signal from gate 8.

More specifically, the input 53 to the discriminating pulse shaper isconnected to a complementary pair, unity gain, buffer amplifierconsisting of NPN transistor 54, PNP transistor 55, bias resistors 56and 57, biasing diodes 58, 58' (which separates the bias of transistors54 and 55 by 1.2 volts) and emitter resistors 59 and 60. A positivepulse at the input 53 results in a positive pulse at base 61 oftransistor 62; likewise a negative pulse at input 53 results in anegative pulse at base 61. When the signal on base 61 exceeds athreshold level, which is determined by the bias on transistor 63 (whichis set by potentiometer 64) the current through transistor 65 is shiftedfrom transistor 63 to 62. Diode pair 66, 66' similar to diode pair 58,58' controls the bias on transistor 65. By this arrangement adifferential comparator is provided whereby the incoming signal for base61 of transistor 62 is compared to a preselected signal level ofpotentiometer 64 and a signal is passed to base 67 of transistor 68 onlyfor those signal inputs which exceed the preselected signal value.

By the shift of current from transistor 63 to transistor 62 a positivepulse is impressed at the base 67 of transistor 68 and the signalinverted and level shifted by transistor 68. The signal is thenreinverted by transistor 69, resulting in a positive pulse at pin 1 ofthe monostable multivibrator 70. Supply voltages 10 volts) which areobtained from voltage divider 71 (comprised of resistors 72 and 73 andcapacitor 74) are applied to pins 2, 4, and 14 of multivibrator 70.

A positive going pulse at pin 1 of multi-vibrator results in a negativepulse at pin 6 and a positive pulse at pin 8, the length of the pulsebeing determined by the resistor capacitor network 75, which iscomprised of resistors 76, 77; capacitors 78, 79; and range switch 80.

A negative control pulse to the sample and hold module 81 causes it tohold the Z input voltage 11 present at that instant for the duration ofthe pulse.

The circuitry of FIG. 3 utilizes standard commercially availablecomponents. Transistors 54 and 69 are type 2N3904; 55 and 68 are type2N3906; 62, 63 and 65 are type 2N3415. Diodes 58, 58' and 66, 66' aretype IN4 l 49. Monostable multivibrator 70 is a 960] integrated circuit.Sample and hold module 81 is a SHI-I-IA available from Analog DevicesInc.

In operation, the sample and hold module 81 is placed between the rampgenerator 10 and the isometric display generator 16 and the positiveoutput from pin 8 of multi-vibrator 70 is connected to pulse generator21. The pulse length of positive and negative outputs of multi-vibrator70 is adjusted to end just prior to the initiation of the next Z rampsignal 11. By this arrangement, the frequency content of the sample andhold module 81 is now no longer dependent upon the ramp signal 11repetition rate but is dependent upon the scanning rate of the X-Yscanner 3 and the nature of the object. These values are, typically, atleast to 1,000 times smaller than the repetition rate of the ramp signal11. Hence, this reduction of required band width considerably reducescomponent requirements and makes high tape playback speeds, such as 60times the recording speed, feasible.

The present invention is particularly useful in the field of imaging inopaque liquids, such as liquid sodium, and thus could be used in LiquidMetal Breeder Reactors as a method for determining the position andcondition of fuel bundles and the detection of foreign objects. Anotherapplication of the present isometric imaging system is fornondestructive testing (imaging of flaws in solids). For thisapplication the present system provides the operator considerably moreinformation as to the true nature, depth and position of scanned objectsthan can be obtained from either B or C conventional scanners.

The detailed description hereinbefore given is intended to beillustrative only. Obviously many variations may be provided by thoseskilled in the art for providing an isometric imaging system withoutdeparting from the intended scope of this invention. For example, thesystem is described with particular reference to an X-Y scanner forindicating the position of the object. Other position indicators, suchas a circular scanner could be used. A circular scanner may, forexample, comprise rotating shaft and disk to which a transducer isattached. The shaft is also translated in one direction, which resultsin the transducer scanning out a helical path. This can be accomplishedmuch faster than X-Y scanning.

Additionally, output amplifiers and offset controls may be incorporatedto provide for magnifying a particular portion of the displayed image,such as that depicting an internal flaw, for detailed study andpositioning it in the center of the display screen.

It is therefore to be understood that the scope of the present inventionis to be determined only in accordance with what is claimed in theappended claims.

What is claimed is:

1. An isometric imaging system for displaying a viewed objectcomprising:

a. means for generating and detecting signals incident to and reflectedfrom said object;

b. means for generating X, Y, and Z output voltages corresponding to thecoordinate position of said object;

c. means for electronically generating coordinates corresponding to anisometric projection of said object from said X, Y, and Z outputvoltages;

(1. means for varying the angular perspective of said isometricprojection;

e. means for displaying said isometric projection; and

f. means for magnetically recording and playing back the signalscorresponding to the isometric projection of said object, so that inconjunction with said means for varying the angular perspective of saidisometric projection, alternate angular perspectives can be readilydisplayed.

2. The apparatus of claim 1 wherein:

a. said means for generating and detecting signals comprises anultrasonic transmitter-receiver, transducer, and an X-Y scanner;

b. said means for electronically generating an isometric projection andsaid means for varying the angular perspective of said projectioncomprises an electronic circuit adapted to receive said X, Y, and Z axisvoltages, to transform same into X, Y coordinates by the formulas:

X =Xcosine 0+ Ysine 0 Y (Y cosine 6) sine Z cos d) where 6 is rotationof the X, Y, axis and 4) is the tilt of the Z axis, and further adaptedto provide variation of angular perspective by varying the parameters 0and d).

3. The apparatus of claim 2 wherein said electronic circuit forgenerating an isometric projection and varying the angular perspectiveof said projection comprises:

a. a sine-cosine potentiometer for analogically generating the functionsnegative sine 0 and negative cosine 0;

b. a second sine-cosine potentiometer for analogically generating thefunctions cosine (i1 and negative sine (I);

c. an operational amplifier for inverting said negative sine 0 functionto produce the function sine 0;

d. a plurality of multiplier means electrically connected to saidsine-cosine potentiometers, said operational amplifier, and said X, Y,and Z voltages to generate the functions negative Y sine 0, negativeXcosine 0, sine 0, negative Ycosine 0, and negative Z cosine 4);

e. a summing operational amplifier electrically connected to saidfunctions negative Y sine 0 and negative X cosine 6 to generate thefunction X X cosine 0 Y sine 0; and

f. further operational amplifier and multiplier means electricallyconnected to said functions X sine 0, negative Y cosine 0, negative sine(I) and negative Z cosine d; to generate the function Y (Y cosine 9Xsine 0) sine Q5 Z cos Q5.

1. An isometric imaging system for displaying a viewed objectcomprising: a. means for generating and detecting signals incident toand reflected from said object; b. means for generating X, Y, and Zoutput voltages corresponding to the coordinate position of said object;c. means for electronically generating coordinates corresponding to anisometric projection of said object from said X, Y, and Z outputvoltages; d. means for varying the angular perspective of said isometricprojection; e. means for displaying said isometric projection; and f.means for magnetically recording and playing back the signalscorresponding to the isometric projection of said object, so that inconjunction with said means for varying the angular perspective of saidisometric projection, alternate angular perspectives can be readilydisplayed.
 2. The apparatus of claim 1 wherein: a. said means forgenerating and detecting signals comprises an ultrasonictransmitter-receiver, transducer, and an X-Y scanner; b. said means forelectronically generating an isometric projection and said means forvarying the angular perspective of said projection comprises anelectronic circuit adapted to receive said X, Y, and Z axis voltages, totransform same into X'', Y'' coordinates by the formulas: X'' X cosinetheta + Y sine theta Y'' (Y cosine theta ) sine phi + Z cos phi wheretheta is rotation of the X, Y, axis and phi is the tilt of the Z axis,and further adapted to provide variation of angular perspective byvarying the parameTers theta and phi .
 3. The apparatus of claim 2wherein said electronic circuit for generating an isometric projectionand varying the angular perspective of said projection comprises: a. asine-cosine potentiometer for analogically generating the functionsnegative sine theta and negative cosine theta ; b. a second sine-cosinepotentiometer for analogically generating the functions cosine phi andnegative sine phi ; c. an operational amplifier for inverting saidnegative sine theta function to produce the function sine theta ; d. aplurality of multiplier means electrically connected to said sine-cosinepotentiometers, said operational amplifier, and said X, Y, and Zvoltages to generate the functions negative Y sine theta , negative Xcosine theta , sine theta , negative Y cosine theta , and negative Zcosine phi ; e. a summing operational amplifier electrically connectedto said functions negative Y sine theta and negative X cosine theta togenerate the function X'' X cosine theta + Y sine theta ; and f. furtheroperational amplifier and multiplier means electrically connected tosaid functions X sine theta , negative Y cosine theta , negative sinephi and negative Z cosine phi to generate the function Y'' (Y cosinetheta -X sine theta ) sine phi + Z cos phi .